Field of the Invention
The invention relates to a method for local heating and global monitoring of a tissue disposed in an imaging device, monitored by the imaging device and heated substantially simultaneously by focused ultrasound. The invention also relates to an apparatus for local heating and global monitoring of a tissue, including an imaging device for receiving the tissue and monitoring the tissue, as well as a source for generating ultrasound.
The invention relates in particular to a method and an apparatus for treating and in particular destroying a selected zone within a tissue in the human body. The tissue is heated for a sufficient length of time, by focusing ultrasound, to a comparatively high temperature sufficient to kill the tissue. The focus of the ultrasound, that is the region in which the energy of the ultrasound attains sufficiently high intensity, is typically approximately 3 mm in diameter and approximately 10 mm in length. If there is a need to treat a larger zone of tissue, then the zone can be divided up into an appropriate grid and treated appropriately by variable focusing of the ultrasound. Both the monitoring of the temperature attained in the zone, and the distribution of that temperature, are of major importance. It is especially critical to prevent the destruction of healthy tissue located immediately adjacent diseased and especially tumorous tissue. Efforts are therefore made to monitor the temperature distribution in a tissue treated with focused ultrasound.
A magnetic resonance scanner with a support for a patient who is to be treated and with a source for focused ultrasound built into the patient support, is sold by the General Electric Company. In that apparatus, complicated provisions for electromagnetic shielding are necessary, in order to prevent the source from impeding the operation of the magnetic resonance scanner itself. A complicated safeguard to protect the patient to be treated against electric currents from the source is also provided.
A paper entitled "Temperature Monitoring of Focused Ultrasound Therapy by MRI", by P. Huber, in Ultrasonics Symposium 1994, pages 1825 ff., describes a combination of a source for focused ultrasound and a magnetic resonance scanner, in which the source and the magnetic resonance scanner are operated in alternation. The magnetic resonance scanner is set up in such a way that it can detect and display both the location of the focus and the temperature distribution in the tissue being treated.
Fundamental information on temperature measurement through the use of magnetic resonance imaging using a contrast medium is found in a paper entitled "Non-Invasive In Vivo Temperature Mapping of Ultrasound Heating using Magnetic Resonance Techniques", by N. B. Smith, in Ultrasonics Symposium 1994, pages 1829 ff.